Preliminary Raw Data - 18O and Precipitation

Aloha everyone!

I wanted to share with you some more of our raw preliminary data. We conducted isotope analysis on six shells (of multiple genera) in Summer 2019, which have given us valuable information about what the environment might have been like at different times at our study site, Ka'ena Point State Park!

For our project, we are conducting isotopic analysis on complete shells gathered from our study site. Full information about how we are preparing shells for isotopic analysis can be found in the Methods tab of our project, under the note "Preparing Shells for Isotopic Analysis."

We will be examining 13C and 18O isotopes in our project, which will tell us about the environmental conditions that our snails lived in thousands of years ago. Today I'm going to focus on what we have learned from our work with 18O isotopes.

 

18O information vs 14C age from six shells gathered from our study site, Ka'ena Point State Park. A lighter isotopic signature indicates heavier, more frequent rainfall or cooler temperatures, while a heavier isotopic signature indicates shorter, less frequent rainfall or hotter temperatures. Isotopic analysis conducted at the Lawrence Livermore National Laboratory in 2019.

For terrestrial snails, oxygen isotopes are primarily affected by two factors: precipitation, and ambient temperature, which work together to affect the oxygen isotope signature of our snail shells. Here's a brief overview of how it works:

The oxygen isotope signature of groundwater is directly impacted by the duration and frequency of rainfall in an area (like our study site, Ka'ena Point!). When raining, the heavier isotope (18O) falls as rain first, and then after some time the lighter isotope (16O) starts to fall. Snails drink this water from pools on the ground, and the isotopes that make up the water are put into their calcium carbonate (CaCO3) shells. Temperature has an impact on the oxygen isotope that our snails take up, as well. When the ambient temperature is hot, the lighter isotope (16O) evaporates first, leaving the heavier isotope in the water for our snails to drink.

That means that in periods of frequent, heavy rainfall, or cooler temperatures/less evaportation, snails are drinking more of the lighter isotope, and incorporating it into their shells. Conversely, when an area receives short bursts of less frequent rainfall, or is hot with high levels of evaporation, more of the heavier isotope is put into in our snails' shells. This means that looking at the oxygen isotope signature of snails' shells can tell us about the precipitation patterns/temperature that our snails were experiencing when they were alive!

Our preliminary data, shown in the graph above, indicates that our snails were taking in more of the heavier isotope as the years went by. The availability of more of the heavy isotope in drinking water could mean that Ka'ena Point was either drying out (less rainfall), or was heating up (more evaporation) as we move towards the present day. Either way, the environment may have been changing to become less habitable for our native Hawaiian snails.

However, six shells is too small a sample size for us to say anything for certain about how the environment may have been changing, which is why we would like to examine more shells. It's also important to note that the change we see form our data so far is taking place over tens of thousands of years, in stark contrast to the climate changes we are seeing take place today. However, we expect that the information we learn from our project, which is examining a period of natural climate change on the Hawaiian island of O'ahu, can help us prepare for changes we may see in the coming years.

Mahalo for reading, and for your support!